In a normal set-up a transparent display screen is provided in front of a user so that they can continue to see the physical world. The display screen is typically a glass waveguide, and a projector is provided to one side. Light from the projector is coupled into the waveguide by a diffraction grating. The projected light is totally internally reflected within the waveguide. The light is then coupled out of the waveguide by another diffraction grating so that it can be viewed by a user. The projector can provide information and/or images that augment a user's view of the physical world.
A challenge exists in the production of wide-screen augmented reality displays because light from an input projector needs to be provided across the entire width of the display (if augmented reality is desired across the full width). One solution is to provide a single input projector with a pupil that extends across the full width of the display. This may require an expensive bespoke projector which is complex to manufacture. An alternative solution is to provide a smaller projector and optics that can expand the field of view across the width of the display. A disadvantage to this approach is that the expansion optics can take up significant space below the display. A further alternative is to provide several input projectors in parallel along the width of the display, which combine to produce the desired augmentation image. A disadvantage to this approach is that gaps between adjacent projectors can produce undesirable optical effects for a viewer.
FIG. 1 is a schematic diagram showing a wide screen augmented reality display 2 and a single input projector 4. Light is projected into a solid angle by each point in the input projector 2, which means that a field of view can be defined for each point. FIG. 1 shows fields of view 6, 8 created by points at opposite edges of the projector 4. The single input projector 4 would fail to project light over the full width of the display 2.
FIG. 2 is a schematic diagram showing the wide screen augmented reality display 2 with a plurality of input projectors 10, 12, 14, 16, 18, 20, 22. The projectors are positioned as close as possible to one another. However, the projectors' supporting structures means that there is a slight gap between the edges of adjacent projectors. The result is a gap between the fields of view of points at adjacent edges of neighbouring projectors. This gap can create undesirable optical effects from the perspective of a viewer. For example, the viewer may observe vertical striping in the display, especially if they change their perspective by turning or moving their head.